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GTL+ INTERFACE SPECIFICATION
12.2.4. System-Based Calculation of Required Input and Output
Timings
Below are two sample calculations. The first determines T
ond determines T
HOLD-MIN
sumptions listed below, with the actual system constraints.
12.2.4.1.
CALCULATING TARGET T
T
and T
can be calculated from the Setup Time equation given earlier in Section
CO-MAX
SU-MIN
12.1.4., "AC Parameters: Flight Time":
T
< T
FLIGHT-MAX
PERIOD-MIN
As an example, for two identical agents located on opposite ends of a network with a flight time
of 7.3 ns, and the other assumptions listed below, the following calculations for T
T
can be done:
SU-MIN
Assumptions:
T
PERIOD-MIN
T
FLIGHT-MAX
T
CLK_SKEW-MAX
T
CLK_JITTER-MAX
T
CO-MAX
T
SU-MIN
Calculation
7.3 < 15 - (T
CO-MAX
T
+T
CO-MAX
SU-MIN
The time remaining for T
fore, in this example, T
CO-MAX
This a numerical example, and does not necessarily apply to any particular
device.
Off-end agents will have less distance to the farthest receiver, and therefore will have shorter
values longer than the example above do not necessarily preclude high-fre-
flight times. T
CO
quency (e.g. 66.6 MHz) operation, but will result in placement constraints for the device, such
as being required to be placed in the middle of the daisy-chain bus.
12-22
. These equations can be used for any system by replacing the as-
CO-MAX
- (T
+ T
CO-MAX
SU-MIN
15 ns
(66.6 MHz)
7.3 ns
(given flight time)
0.7 ns
(0.5ns for clock driver)
(0.2 ns for board skew)
0.2 ns
(Clock phase error)
?? ns
(Clock to output data time)
?? ns
(Required input setup time)
+T
+0.7 +0.2)
SU-MIN
< 6.8 ns
and T
can be split ~60/40% (recommendation). There-
CO-MAX
SU-MIN
would be 4.0 ns, and T
NOTE
and T
CO-MAX
SU-MIN
, AND T
SU-MIN
+ T
+T
CLK_SKEW-MAX
CLK_JITTER-MAX
2.8 ns.
SU-MIN
, while the sec-
)
and
CO-MAX
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